1. Field of Invention
The present invention relates generally to a valve for performing a medical embolizing treatment, and particularly to a valve that increases penetration of a treatment agent into targeted blood vessels and reduces reflux of the treatment agent into non-targeted vessels.
2. State of the Art
Embolization, chemo-embolization, and radio-embolization therapy are often clinically used to treat a range of diseases, such as hypervascular liver tumors, uterine fibroids, secondary cancer metastasis in the liver, pre-operative treatment of hypervascular menangiomas in the brain and bronchial artery embolization for hemoptysis. An embolizing agent may be embodied in different forms, such as beads, liquid, foam, or glue placed into an arterial vasculature. The beads may be uncoated or coated. Where the beads are coated, the coating may be a chemotherapy agent, a radiation agent or other therapeutic agent. When it is desirable to embolize a small blood vessel, small bead sizes (e.g., 10 μm-100 μm) are utilized. When a larger vessel is to be embolized, a larger bead size (e.g., 100 μm-900 μm) is typically chosen.
While embolizing agent therapies which are considered minimally or limited invasive have often provided good results, they have a small incidence of non-targeted embolization which can lead to adverse events and morbidity. Infusion with an infusion microcatheter allows bi-directional flow. That is, the use of a microcatheter to infuse an embolic agent allows blood and the infused embolic agent to move forward in addition to allowing blood and the embolic agent to be pushed backward (reflux). Reflux of a therapeutic agent causes non-target damage to surrounding healthy organs. In interventional oncology embolization procedures, the goal is to bombard a cancer tumor with either radiation or chemotherapy. It is important to maintain forward flow throughout the entire vascular tree in the target organ in order to deliver therapies into the distal vasculature, where the therapy can be most effective. This issue is amplified in hypovascular tumors or in patients who have undergone chemotherapy, where slow flow limits the dose of therapeutic agent delivered and reflux of agents to non-target tissue can happen well before the physician has delivered the desired dose.
The pressure in a vessel at multiple locations in the vascular tree changes during an embolic infusion procedure. Initially, the pressure is high proximally, and decreases over the length of the vessel. Forward flow of therapy occurs when there is a pressure drop. If there is no pressure drop over a length of vessel, therapy does not flow downstream. If there is a higher pressure at one location, such as at the orifice of a catheter, the embolic therapy flows in a direction toward lower pressure. If the pressure generated at the orifice of an infusion catheter is larger than the pressure in the vessel proximal to the catheter orifice, some portion of the infused embolic therapy travels up stream (reflux) into non-target vessels and non-target organs. This phenomenon can happen even in vessels with strong forward flow if the infusion pressure (pressure at the orifice of the catheter) is sufficiently high.
During an embolization procedure, the embolic agents clog distal vessels and block drainage of fluid into the capillary system. This leads to an increase in the pressure in the distal vasculature. With the increased pressure, there is a decrease in the pressure gradient and therefore flow slows or stops in the distal vasculature. Later in the embolization procedure, larger vessels become embolized and the pressure increases proximally until there is a system that effectively has constant pressure throughout the system. The effect is slow flow even in the larger vessels, and distally the embolic agent no longer advances into the target (tumor).
In current clinical practice with an infusion catheter, the physician attempts to infuse embolics with pressure that does not cause reflux. In doing this, the physician slows the infusion rate (and infusion pressure) or stops the infusion completely. The clinical impact of current infusion catheters and techniques is two fold: low doses of the therapeutic embolic is delivered and there is poor distal penetration into the target vessels.
Additionally, reflux can be a time-sensitive phenomenon. Sometimes, reflux occurs as a response to an injection of the embolic agent, where the reflux occurs rapidly (e.g., in the time-scale of milliseconds) in a manner which is too fast for a human operator to respond. Also, reflux can happen momentarily, followed by a temporary resumption of forward flow in the blood vessel, only to be followed by additional reflux.
FIG. 1 shows a conventional (prior art) embolization treatment in the hepatic artery 106. Catheter 101 delivers embolization agents (beads) 102 in a hepatic artery 106, with a goal of embolizing a target organ 103. It is important that the forward flow (direction arrow 107) of blood is maintained during an infusion of embolization agents 102 because the forward flow is used to carry embolization agents 102 deep into the vascular bed of target organ 103.
Embolization agents 102 are continuously injected until reflux of contrast agent is visualized in the distal area of the hepatic artery. Generally, since embolization agents 102 can rarely be visualized directly, a contrast agent may be added to embolization agents 102. The addition of the contrast agent allows for a visualization of the reflux of the contrast agent (shown by arrow 108), which is indicative of the reflux of embolization agents 102. The reflux may, undesirably, cause embolization agents 102 to be delivered into a collateral artery 105, which is proximal to the tip of catheter 101. The presence of embolization agents 102 in collateral artery 105 leads to non-target embolization in a non-target organ 104, which may be the other lobe of the liver, the stomach, small intestine, pancreas, gall bladder, or other organ.
Non-targeted delivery of the embolic agent may have significant unwanted effects on the human body. For example, in liver treatment, non-targeted delivery of the embolic agent may have undesirable impacts on other organs including the stomach and small intestine. In uterine fibroid treatment, the non-targeted delivery of the embolic agent may embolize one or both ovaries leading to loss of menstrual cycle, subtle ovarian damage that may reduce fertility, early onset of menopause and in some cases substantial damage to the ovaries. Other unintended adverse events include unilateral deep buttock pain, buttock necrosis, and uterine necrosis.
Often, interventional radiologists try to reduce the amount and impact of reflux by slowly releasing the embolizing agent and/or by delivering a reduced dosage. The added time, complexity, increased x-ray dose to the patient and physician (longer monitoring of the patient) and potential for reduced efficacy make the slow delivery of embolization agents suboptimal. Also, reducing the dosage often leads to the need for multiple follow-up treatments. Even when the physician tries to reduce the amount of reflux, the local flow conditions at the tip of the catheter change too fast to be controlled by the physician, and therefore rapid momentary reflux conditions can happen throughout infusion.
U.S. Pat. No. 8,696,698, previously incorporated herein, describes a microvalve infusion system for infusing an embolic agent to a treatment site in a manner that overcomes many of the issues previously identified with infusion using an infusion catheter alone. Referring to prior art FIGS. 2A and 2B, the microvalve infusion system 200 includes a dynamically adjustably filter valve 202 coupled to the distal end of a delivery catheter 204. The delivery catheter and filter valve extend within an outer catheter 206. The filter valve 202 is naturally spring biased by its construction of filamentary elements 208 to automatically partially expand within a vessel when it is deployed from the outer catheter 206, and is coated with a polymer coating 210 that has a pore size suitable to filter an embolic therapeutic agent. More particularly, the filter valve 202 has an open distal end 212 and is coupled relative to the delivery catheter 204 such that an embolic agent infused through the delivery catheter 204 and out of the distal orifice 214 of the delivery catheter 204 exits within the interior 216 of the filter valve. In view of this construction, upon infusion, an increase in fluid pressure results within the filter valve and causes the filter valve 202 to open, extend across a vessel, and thereby prevent reflux of the infused embolic agent. In addition, as the fluid is pressurized through the delivery catheter and into the filter valve, the downstream pressure in the vessel is increased which facilitates maximum uptake into the target tissue for therapeutically delivered agents. Further, the filter valve is responsive to local pressure about the valve which thereby enables substantially unrestricted forward flow of blood in the vessel, and reduces or stops reflux (regurgitation or backward flow) of embolization agents which are introduced into the blood.
However, the devices in U.S. Pat. No. 8,696,698 have certain issues that may not always be advantageous. In various disclosed FIGS. 44, the devices shown have a large distal diameter which limits trackability in tortuous branching vasculature. The distal end of the device in a collapsed, undeployed state is defined by the size of an outer catheter 206, which can be significantly larger than the outer diameter delivery catheter 204 that supports the filter valve 202 and significantly larger than the outer diameter of a guidewire (not shown) used to the guide the microvalve to the target location within the vessel. As such, tracking the filter valve into the smaller vascular branches does not have a desired reliability. In addition, once the device is tracked to a treatment location, deployment of the filter valve requires that the frictional force between the filter valve and the outer catheter be overcome. Overcoming such forces can potentially abrade the polymer coating on the filter valve. Improvements to such designs was provided in other figures disclosed in U.S. Pat. No. 8,696,698, so that the outer diameter of the distal aspect of the device is reduced in size to in a manner that would faciliate tracking. However, once any of the embodiments of filter valve 202 in U.S. Pat. No. 8,696,698 are shown in the open configuration, they assumes the shape of an open frustocone, which allows refluxing therapeutic embolic agent to enter the valve. This may lead to therapeutic agent remaining in the filter valve, particularly under conditions of slow forward flow within the vessel, which potentially could result in incomplete dosing.